Brains evolve gradually over a lifetime—good news for parents. During the first years the infant brain develops very quickly: language, cognition, perception, and the major behavioral systems are put into place, but it is the fine-tuning of these systems throughout life that ultimately accounts for who a person is. (Restak, Richard, MD. The Secret Life of the Brain. D.C.: The Dana Press and Joseph Henry Press, 2001, p Ix)

See Plasticity (below).